First tube amp build: Fender Deluxe AB763 style amp (no reverb).

[mikepukmel]

I'm no Roy Blankenship.

Yet!

[bob p]

you can use a smaller gauge of wire on the noval tubes than on the octal tubes because they'll draw a lot less heater current.

i'd use heavier wires from the PT to the power tubes, and lighter wires to the preamp tubes.

solid wire stays where you put it and it doesn't put up a fight when it's time to thread the needle.

[mikepukmel]

Thanks everyone. My eye sight is so crappy, I had the two wires through, but one strand was bent down and I thought it was not through the loop, but it was. Heh, Mr Magoo's amp project!

[mikepukmel]

I managed to get the heater wiring done up to, not incl the pilot light. The Hammond doesn't have a center tap on the 6.3V line, so have to figure out where to put a few resistors in. Aside from that, it didn't come out nearly as nice as I wanted, but its not horrible. At least, I don't think it is. Ran the "ohm meter/gentle connection jiggle" connection test, didn't find any shorts to ground, and connections seem to be covered with solder, and didn't find any cold joints. The rest should be easier, I think.

[mikepukmel]

They will all look about the same. OK, so one wire fits? Great. First, you might be using oversize wire, no need for #12 wire in an amp. But if two wires won't, fit try this. Bare the wire to go into it a little extra longer. Now strip the second wire and wrap it around the first up next to the insulation. The extra length you stripped will now still poke into the socket tab. Solder all.

But really, I'd just knock the wire size down a notch. 20 is plenty.

Thanks! I think the wire I got, fits, if the cut and strip job is perfect. My wire cutter leaves a little tiny bendy part on the end if Im not careful and that catches on the hole in the pin. I tried a combination of your suggestion and Justin's, and it works. Definitely the last socket was a lot easier than the first. Skills improving.

Some web page someplace (might have been not good info), said to put 18 to the first two output tubes, then switch to 20 for the rest of the 9 pins. Is it OK to do it that way? its only a 22 watt or so amp. maybe the bigger amps need beefier wire?

[Justin Thomas]

If you're using a Fender-style pilot light, they usually run the resistors to ground right by the light... or on the same ground as the bias supply.

Justin

[mikepukmel]

you can use a smaller gauge of wire on the noval tubes than on the octal tubes because they'll draw a lot less heater current.

i'd use heavier wires from the PT to the power tubes, and lighter wires to the preamp tubes.

solid wire stays where you put it and it doesn't put up a fight when it's time to thread the needle.

Oops, I asked the question you answered exactly. Thanks! That would do it. The 18 fits easily into the two holes in the pins on the 8 pin socket. The 20 fits easily into the 9 pin sockets. !!

[mikepukmel]

[mikepukmel]

If you're using a Fender-style pilot light, they usually run the resistors to ground right by the light... or on the same ground as the bias supply.

Justin

Thanks Justin. The holes in the hook up tabs on the pilot light are pretty big, can I just solder one end to the tabs on the light itself, and the other end to a blob of solder on the chassis right below that?

[mikepukmel]

Bing! They really dd this from the factory? Looks like the two artificial center tap resistors go to a lug mounted on one of the transformer bolts. Would this loosen up over time? Maybe a dot of loctite on that one keps nut.

[mikepukmel]

Don't worry too much -- my post was intended to be guidance for a layout, not an expectation that you'd rip apart an existing layout and start over.

Not all resistors generate enough heat to be troublemakers, so you don't have to reposition every component if your layout is already done. Just look at the resistors that dissipate power (generate heat) and be careful not to snug the electrolytic caps up against them.

In a cathode biased amp the 6V6 cathodes would be important. That's not a concern with fixed bias 6V6. It's good practice to think about resistor heat when you do the layout for your noval tubes, but not as critical since they draw less power, generate less heat and aren't likely to cause immediate cap failures.

Bob, since I don't have the chops to be able to calculate current/voltage and so power throughout the circuit, can I go by the wattage of the resistor to guess which ones will put off more heat? There are a couple of big 470R resistors around the 6V6's, but all of the other resistors on the main board are 1/2 watt. And the original boards seem to cram the 'brown turd' or blue signal caps right on top of the other components (caps and resistors), can I assume those will run relatively cold, unless of course some kind of failure?

[mikepukmel]

A friend (who doesn't live locally) suggested moving the 68k resistors that Fender mounted on the input jacks, to the input tubes. That they would work better as grid stop's if mounted on the tube socket tabs. Ive seen some of your (guru) builds look like that. Can I replace the 2 resistors with one, of some value, run one shielded wire from the end of that resistor to the input jacks, or should I use the two 68ks, and run two shielded wires, each to its own input jack for the given channel? Ive read explanations over my head, about the exact function of the grid stops, radio wave rejection, but more important, changing the time constant to help prevent or reduce blocking distortion, and also helping to reduce the chance of parasitic oscillation. Since the original blackface amps are not noted for having oscillation problems, that I know of, but they do 'fart out' if you crank up the bass and volume, wondering what effect moving the resistors would have on unwanted oscillation and blocking disto.

[Justin Thomas]

Yes, they really did do that from the factory. Personally, if that grounding scheme is good enough for them, it's good enough for me as far as noise is concerned. I don't see anything wrong with your idea either. What I <won't> do is tie my Safety Earth to a transformer bolt.

Though normally when I build I run the heater CT, HT CT, reservoir cap, etc., all to one point and all my others to another point. But I'm never using an established layout, so I'm more cautious from the get-go.

Justin

[mikepukmel]

Yes, they really did do that from the factory. Personally, if that grounding scheme is good enough for them, it's good enough for me as far as noise is concerned. I don't see anything wrong with your idea either. What I <won't> do is tie my Safety Earth to a transformer bolt.

Though normally when I build I run the heater CT, HT CT, reservoir cap, etc., all to one point and all my others to another point. But I'm never using an established layout, so I'm more cautious from the get-go.

Justin

Thanks Justin! Scouring the web for photos again this morning over my oatmeal, I found another photo of a 70's fender amp, where they put a lug on one of the transformer posts and soldered the safety ground wire to that, but also put a bead of solder around the edge of the lug to the chassis. I'm guessing you said you'd never put the safety ground on the transformer bolt since it could loosen up and cause a hazard? Oh man I remember getting zapped a few times with my old blackface Princeton Reverb, two wire cord, no ground, and in a very, very old house with knob and tube wiring, mostly ungrounded. I would not wish that on my worst enemy.

[Leo_Gnardo]

you'd never put the safety ground on the transformer bolt since it could loosen up and cause a hazard?

Although that's not the best practice, I've seen it done often, and with factory builds. Since you have that big 80W iron, there's no reason the AC power ground can't be directly soldered to chassis. I generally do that on the strip between power transformer and chassis side gusset. It helps to scrub the chassis surface with wire brush or 600 grit paper or crocus, also apply a dab of Nokorode or similar flux for a solid connection.